Semiconductor memory devices generally include arrays of cells that form memory units. Each of the cells can include a transistor pattern having a gate and source/drain regions. To obtain ever higher integration density in the memory devices, gate lengths and intervals between gates are continuing to be reduced. For example, in some memory-devices the source/drain regions can have a width of less than several tens of nanometers.
The small size of some transistor patterns may cause them to be difficult to observe with an optical microscope. Consequently, it can be difficult to detect and identify a particular failed cell in a memory device. For example, it may not be feasible to optically count numerous small cells in a memory device in an attempt to determine an address of a failed cell. Moreover, when a cell region has failed because of a doping abnormality, such a failure may be difficult to optically observe because the region may appear optically identical to other normal regions.
One approach to analyzing memory cells or other device features is to expose a vertical profile of a cell that is to be analyzed. For example, it can be desirable to obtain a vertical profile of a failed cell address in a memory device by grinding a side face of the memory device to expose regions of the failed cell address. However, it may not be feasibly to optically identify a failed cell address with the memory device, and then to expose regions of that particular cell address so that they may be further analyzed.
A cell region can be inspected with a scanning microscope (SCM). A SCM can include a capacitance sensor and a probe. The capacitance sensor is electrically connected to the probe for measuring a capacitance between the probe and the cell region. The probe and cell region may, for example, have nanometer feature sizes. The capacitance sensor includes a high-frequency oscillator and an electrical resonator. The capacitance, which can have a very low value, is measured by varying a resonance frequency that is based on the capacitance. For example, a high frequency measured signal can be modulated onto a low frequency signal. A differential value of the capacitance relative to a voltage may be measured using a lock-in amplifier. The SCM can measure carrier concentrations and second dimensional doping profiles of the cell regions.
Accordingly, if a failed cell region can be exposed for analysis by a SCM, the doping profiles measured by the SCM may provide an answer as to why the cell region failed.